80-Bus News

      {Reduce the size of the box being drawn.}
      lox := lox+i; loy := loy+t;
      hix := hix-1; hiy := hiy-1
    END
  UNTIL loy = hiy;
  {Which means we have reached the middle, almost!
  The next bit fills in the remaining blank line.}
  FOR i := lox TO hix BO
    BEGIN
      GRAPH(col,i,loy);
      FOR j := 1 TO 10 DO BEGIN END
    END
END;
PROCEDURE spiralwipe;
BEGIN
  spiral(on);
  spiral(off)
END;

The procedure is called by including the word “spiralwipe” in your program, this spirals round twice. The first time round, all the pixels making up the spiral are switched on, and on the second spiral, they are switched off. Alternatively, you can use the call

spiral(invert);

which will spiral round the screen just once, inverting all the graphics characters as it goes. Once again, impress your friends…

Medium sized review of a large book.

I don’t think Rory has done this one yet, although it’s a mystery how he gets through so many! This is about “Microcomputer Architecture and Programming” by John F. Wakerly, which is published by Wiley. It is the last book I bought from the Computer Book Club, before I told them I had had enough of their methods. (See last vitriolic episode for the boring details…)

Anyway, as I said, this is a large book, with 692 pages. The author describes the book as being suitable for an introductory course on (micro) computer organisation and assembly language programming. Since it is so large, I have read only a few chapters so far. I do like the style, which is somewhat like a transatlantic version of P.J.Brown. Reviews are allowed to contain reasonably sized chunks from the book in question, so here is an example, from chapter 3, which is headed “Data Structures in Pascal Programs.”

“Niklaus Wirth, the designer of Pascal, has written a programming textbook called “Algorithms + Data Structures = Programs”. From the previous chapter, you should already have a good idea of what programs and algorithms are. To find out what data structures are, just subtract, and you don’t have to read this chapter…”

The two chapters before that give a review of “fundamental concepts” and Pascal respectively. They are good, although the experienced reader will be able to skip through them pretty fast. The greater part of the book, as yet unread in detail, I have to describe by glancing at it, or reading the description at the start of the book. There are four chapters in the first, “introductory and remedial”, part of the book. Part 2 describes basic principles that apply to all computers, using as examples two hypothetical processors, which just happen to have instruction sets and features that are subsets of those of the Motorola 6809 and the Zilog 28000. I wanted to learn more about the 28000, so I have looked ahead to the section concerned, and it seems very comprehensive, not to mention comprehensible.